This invention relates to planetary gearing systems and more particularly to structures for positioning and retaining a planet gear carrier therein.
Planetary gearing systems are used in a variety of mechanisms in which rotary drive is to be transmitted while realizing a speed reduction or speed increase accompanied by a torque increase or reduction. The drive arrangements between a fluid motor and a wheel of a vehicle is one example of mechanism in which planetary gearing systems are often used. While planetary gearing systems may take a variety of specific forms, all have in common a planet gear carrier supported for rotation about a primary axis and carrying one or more planet gears which may orbit about the primary axis while also being rotatable about a secondary orbiting axis which is parallel to the primary axis. Depending on the type of planetary gearing system, the planet gears may engage one or both of a sun gear and a ring gear which are both disposed coaxially with respect to the primary axis.
In instances where sizable torque loads must be transmitted through a planetary gearing system, it is a common practice to include more than one planet gear on the carrier. The presence of the additional planet gears does not change the basic functions of the system insofar as speed reductions or speed increases are concerned but do serve to avoid the severe concentration of stress at a limited number of gear teeth, bearings and the like which may occur in a planetary gearing system having a single planet gear.
If the planetary gear carrier is journaled to some other component of the mechanism through conventional bearing means or the like so that it has little if any opportunity to shift radially and axially, then this objective of equally distributing stresses between the several planet gears is imperfectly realized at least at times. This would not be true in theory if the components of the system were manufactured with absolutely exact predetermined dimensions and were located in the planetary gearing system at absolutely exact predetermined positions, but this kind of absolute precision does not usually exist as a practical matter. The gears, bearings, axles and other elements of the system will, as a practical matter, vary somewhat from their theoretical proportions, dimensions and orientations and in any real system the rotational axes, orientations and configurations of such elements will vary slightly from what the designer originally specified.
Because of these factors, at any given moment in a planetary system having a positionally fixed carrier most of the structural stress may be concentrated on a particular one of the plurality of planet gears and on a single particular small segment of the associated sun gear and ring gear while the other planet gears are carrying less than their theoretical share of the load. This concentration of stress may shift from one planet gear to another in the course of a single revolution of the carrier depending on the nature of the departure of the proportions and position of the various parts from the theoretical ideal.
To counteract the adverse unequal distribution of stress loads discussed above, it is a known practice to employ what is termed a floating planet carrier. In such systems the planet gear carrier is not journaled by ordinary bearing means so that it is not rigidly constrained against radial and axial movements. Instead, the planet gears and thus the carrier are essentially supported and positioned by the associated sun gear and ring gear with which the planet gears are engaged. With this arrangement, an incipient unequal distribution of stress loads between the several planet gears tends to be self-correcting. Such a stress concentration inherently acts to shift the planet gears and associated carrier slightly in the radial direction or to tilt the planet gear and carrier assembly relative to the rotational axis to a small degree in such a manner as to tend to maintain an equal distribution of load between the several planet gears.
Where the planet gears and carrier are capable of floating as described above, it is usually necessary to provide means for establishing maximum limits to the positional shifting of the floating components. Where the planet gears engage both a sun gear and a ring gear, movement of the carrier in the radial direction may be inherently limited. However, there may not be any inherent constraint against excessive axial movement of the carrier and planet gears and therefore some kind of retaining or motion-limiting means must be provided. The structures heretofore utilized for such purposes have been effective to establish the desired limits of movement but have been so constituted as to create unnecessary friction with consequent acceleration of wear, unnecessary dissipation of power and unnecessary heating of components of the system.